When manufacturing a heat exchanger used in an air conditioner or the like, as depicted in FIG. 5A, a U-shaped heat exchanger tube 106 is normally inserted into a plurality of collar-equipped holes that are formed in each fin 100 of a fin layer produced by stacking a plurality of fins 100.
Since gaps exist between the inserted heat exchanger tube 106 and the inner wall surfaces of the collar-equipped holes 102, primary tube expansion is carried out by inserting a tube expanding billet 108 depicted in FIG. 5A into the heat exchanger tube 106 to expand straight portions 106a of the heat exchanger tube 106 and thereby integrate the heat exchanger tube 106 with the fins 100. When doing so, a hairpin portion 106b of the heat exchanger tube 106 that protrudes from a lower end surface of the fin layer 104 is supported by a support portion 116.
In addition, a front end portion of a flare punch 110 depicted in FIG. 5A is inserted into front end portions of the heat exchanger tube 106 that has been subjected to primary tube expansion to carry out secondary tube expansion that further increases the diameter of the front end portions of the heat exchanger tube 106 that has been subjected to primary tube expansion and the vicinity thereof and thereby form expanded-diameter portions 112 and also form flare portions 114 in front end portions of the expanded-diameter portions 112.
As depicted in FIG. 5B, one end portion of a curved connecting portion 120 for connecting to an adjacent U-shaped heat exchanger tube 106 is inserted into an expanded-diameter portion 112 and a flare portion 114 that have been formed in this way.
As one example, a tube expanding apparatus 200 depicted in FIG. 6 and disclosed in Patent Document 1 given below is known as a tube expanding apparatus that carries out tube expansion on the heat exchanger tube 106 depicted in FIG. 5. The tube expanding apparatus 200 depicted in FIG. 6 is equipped with a pressing plate 206 to which rear end portions of a plurality of mandrels 202, 202 are attached and which is provided so as to be capable of being raised and lowered in the up-down direction by cylinder apparatuses 204, 204 as driving means, a flare platform 210 that is suspended from the pressing plate 206 by rod members 208, 208, balancers 212, 212 that are provided below the flare platform 210, contact the flare platform 210 that has been lowered together with the pressing plate 206, and support the flare platform 210 at a predetermined position, and a contact platform 216 that is provided at a predetermined position on a support structure 214 that extends upward from the flare platform 210 so as to contact the lowered pressing plate 206 in a state where the flare platform 210 is being supported at a predetermined position by the balancers 212, 212.
A tube expanding billet 108 as depicted in FIG. 5A is attached to each front end portion of the mandrels 202, 202 and flare punches 110 as depicted in FIG. 5A are attached to the flare platform 210.